Microsoft Word C034565e doc Reference number ISO 21528 1 2004(E) © ISO 2004 INTERNATIONAL STANDARD ISO 21528 1 First edition 2004 08 15 Microbiology of food and animal feeding stuffs — Horizontal meth[.]
INTERNATIONAL STANDARD ISO 21528-1 First edition 2004-08-15 `,,,,,,-`-`,,`,,`,`,,` - Microbiology of food and animal feeding stuffs — Horizontal methods for the detection and enumeration of Enterobacteriaceae — Part 1: Detection and enumeration by MPN technique with pre-enrichment Microbiologie des aliments — Méthodes horizontales pour la recherche et le dénombrement des Enterobacteriaceae — Partie 1: Recherche et dénombrement l'aide de la technique NPP avec préenrichissement Reference number ISO 21528-1:2004(E) Copyright International Organization for Standardization Reproduced by IHS under license with ISO No reproduction or networking permitted without license from IHS © ISO 2004 Not for Resale ISO 21528-1:2004(E) PDF disclaimer This PDF file may contain embedded typefaces In accordance with Adobe's licensing policy, this file may be printed or viewed but shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing In downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy The ISO Central Secretariat accepts no liability in this area Adobe is a trademark of Adobe Systems Incorporated Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation parameters were optimized for printing Every care has been taken to ensure that the file is suitable for use by ISO member bodies In the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below © ISO 2004 All rights reserved Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISO's member body in the country of the requester ISO copyright office Case postale 56 • CH-1211 Geneva 20 Tel + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyright@iso.org Web www.iso.org Published in Switzerland `,,,,,,-`-`,,`,,`,`,,` - ii Copyright International Organization for Standardization Reproduced by IHS under license with ISO No reproduction or networking permitted without license from IHS © ISO 2004 – All rights reserved Not for Resale ISO 21528-1:2004(E) Contents Page Foreword iv Introduction v Scope Normative references Terms and definitions 4.1 4.2 Principle Detection of Enterobacteriaceae (see Annex A) Enumeration by the MPN technique (see Annex B) Diluent, culture media and reagent Apparatus and glassware 7 Sampling Preparation of test sample 9.1 9.2 9.3 9.4 9.5 9.6 Procedure General Detection method Enumeration method (MPN method) Isolation and selection for confirmation Subculturing selected colonies Biochemical confirmation tests 10 10.1 10.2 10.3 Expression of results Confirmed positive tubes Detection method 10 Enumeration method: Calculation of the most probable number (MPN) 10 11 Precision 10 12 Test report 10 Annex A (normative) Diagram of procedure of the detection method 11 Annex B (normative) Diagram of procedure for MPN technique 12 `,,,,,,-`-`,,`,,`,`,,` - iii © ISO 2004 – All rights reserved Copyright International Organization for Standardization Reproduced by IHS under license with ISO No reproduction or networking permitted without license from IHS Not for Resale ISO 21528-1:2004(E) Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies) The work of preparing International Standards is normally carried out through ISO technical committees Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part The main task of technical committees is to prepare International Standards Draft International Standards adopted by the technical committees are circulated to the member bodies for voting Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights ISO shall not be held responsible for identifying any or all such patent rights This first edition of ISO 21528-1, together with ISO 21528-2, cancels and replaces the following standards: ISO 5552:1997, Meat and meat products — Detection and enumeration of Enterobacteriaceae without resuscitation — MPN technique and colony-count technique; ISO 7402:1993, Microbiology — General guidance for the enumeration of Enterobacteriaceae without resuscitation — MPN technique and colony-count technique; `,,,,,,-`-`,,`,,`,`,,` - ISO 8523:1991, Microbiology — General guidance for the detection of Enterobacteriaceae with preenrichment ISO 21528-1 was prepared by Technical Committee ISO/TC 34, Food products, Subcommittee SC 9, Microbiology ISO 21528 consists of the following parts, under the general title Microbiology of food and animal feeding stuffs — Horizontal methods for the detection and enumeration of Enterobacteriaceae: Part 1: Detection and enumeration by MPN technique with pre-enrichment Part 2: Colony-count method iv Copyright International Organization for Standardization Reproduced by IHS under license with ISO No reproduction or networking permitted without license from IHS © ISO 2004 – All rights reserved Not for Resale ISO 21528-1:2004(E) Introduction `,,,,,,-`-`,,`,,`,`,,` - This part of ISO 21528 is intended to provide general guidance for the examination of products not dealt with by existing International Standards and to be taken into account by organizations preparing microbiological test methods for application to foods or animal feeding stuffs Because of the large variety of products within this field of application, these guidelines may not be appropriate in every detail for certain products, and for some other products it may be necessary to use different methods Nevertheless, it is hoped that in all cases every attempt will be made to apply the guidelines provided as far as possible and that deviations from them will only be made if absolutely necessary for technical reasons When this part of ISO 21528 is next reviewed, account will be taken of all information then available regarding the extent to which the guidelines have been followed and the reasons for deviation from them in the case of particular products The harmonization of test methods cannot be immediate, and for certain groups of products International Standards and/or national standards may already exist that not comply with this horizontal method It is hoped that when such standards are reviewed they will be changed to comply with this part of ISO 21528 so that eventually the only remaining departures from this horizontal method will be those necessary for wellestablished technical reasons v © ISO 2004 – All rights reserved Copyright International Organization for Standardization Reproduced by IHS under license with ISO No reproduction or networking permitted without license from IHS Not for Resale `,,,,,,-`-`,,`,,`,`,,` - Copyright International Organization for Standardization Reproduced by IHS under license with ISO No reproduction or networking permitted without license from IHS Not for Resale INTERNATIONAL STANDARD ISO 21528-1:2004(E) Microbiology of food and animal feeding stuffs — Horizontal methods for the detection and enumeration of Enterobacteriaceae — Part 1: Detection and enumeration by MPN technique with pre-enrichment Scope This part of ISO 21528 specifies a method, with pre-enrichment, for the detection of Enterobacteriaceae It is applicable to products intended for human consumption and the feeding of animals, and environmental samples in the area of food production and food handling Enumeration is carried out by calculation of the most probable number (MPN) after incubation at 37 °C 1) (or 30 °C) in liquid medium This method is applicable when the microorganisms sought are expected to need resuscitation before enrichment, and when the number sought is expected to be in the range to 100 per millilitre or per gram of test sample A limitation on the applicability of this part of ISO 21528 is imposed by the susceptibility of the method to a large degree of variability (see Clause 11) Normative references ISO 6887-1:1999, Microbiology of food and animal feeding stuffs — Preparation of test samples, initial suspension and decimal dilutions for microbiological examination — Part 1: General rules for the preparation of the initial suspension and decimal dilutions 1) The temperature of 37 °C is generally used when the enumeration of Enterobacteriaceae is for a hygienic indicator Alternatively, a temperature of 30 °C can be chosen when the enumeration of Enterobacteriaceae is conducted for technological purposes and includes psychrotrophic Enterobacteriaceae © ISO 2004 – All rights reserved Copyright International Organization for Standardization Reproduced by IHS under license with ISO No reproduction or networking permitted without license from IHS Not for Resale `,,,,,,-`-`,,`,,`,`,,` - The following referenced documents are indispensable for the application of this document For dated references, only the edition cited applies For undated references, the latest edition of the referenced document (including any amendments) applies ISO 21528-1:2004(E) ISO 6887-2, Microbiology of food and animal feeding stuffs — Preparation of test samples, initial suspension and decimal dilutions for microbiological examination — Part 2: Specific rules for the preparation of meat and meat products ISO 6887-3, Microbiology of food and animal feeding stuffs — Preparation of test samples, initial suspension and decimal dilutions for microbiological examination — Part 3: Specific rules for the preparation of fish and fishery products ISO 6887-4, Microbiology of food and animal feeding stuffs — Preparation of test samples, initial suspension and decimal dilutions for microbiological examination — Part 4: Specific rules for the preparation of products other than milk and milk products, meat and meat products, and fish and fishery products ISO 7218:1996, Microbiology of food and animal feeding stuffs — General rules for microbiological examinations ISO 8261, Milk and milk products — General guidance for the preparation of test samples, initial suspensions and decimal dilutions for microbiological examination ISO/TS 11133-2:2003, Microbiology of food and animal feeding stuffs — Guidelines on preparation and production of culture media — Part 2: Practical guidelines on performance testing of culture media Terms and definitions For the purposes of this document, the following terms and definitions apply 3.1 Enterobacteriaceae microorganisms that form characteristic colonies on violet red bile glucose agar and that ferment glucose and show a negative oxidase reaction when the tests are carried out in accordance with the methods specified in this part of ISO 21528 3.2 detection of Enterobacteriaceae determination of the presence or absence of these bacteria, in a particular quantity of product, when tests are carried out in accordance with this part of ISO 21528 3.3 enumeration of Enterobacteriaceae most probable number of Enterobacteriaceae found per millilitre or per gram of the test sample when the test is carried out according to the method specified in this part of ISO 21528 Principle 4.1 4.1.1 Detection of Enterobacteriaceae (see Annex A) Pre-enrichment in non-selective medium Buffered peptone water (BPW) is inoculated with the test portion, then incubated at 37 °C (or 30 °C)1) for 18 h ± h Copyright International Organization for Standardization Reproduced by IHS under license with ISO No reproduction or networking permitted without license from IHS © ISO 2004 – All rights reserved Not for Resale `,,,,,,-`-`,,`,,`,`,,` - ISO/TS 11133-1, Microbiology of food and animal feeding stuffs — Guidelines on preparation and production of culture media — Part 1: General guidelines on quality assurance for the preparation of culture media in the laboratory ISO 21528-1:2004(E) 4.1.2 Enrichment in selective liquid medium The enrichment broth [buffered brilliant green bile glucose broth (EE broth)] is inoculated with the culture obtained after pre-enrichment, then incubated at 37 °C (or 30 °C)1) for 24 h ± h Isolation and selection for confirmation A selective solid medium (violet red bile glucose agar) is inoculated with the culture obtained after enrichment in EE broth, then incubated at 37 °C (or 30 °C)1) It is examined after 24 h ± h to check for the presence of colonies presumed by their characteristics to be Enterobacteriaceae 4.1.4 Confirmation Colonies of presumptive Enterobacteriaceae are subcultured onto non-selective medium, and confirmed by means of tests for the fermentation of glucose and the presence of oxidase 4.2 Enumeration by the MPN technique (see Annex B) 4.2.1 Pre-enrichment in non-selective medium A test portion of x g is added to x ml of buffered peptone water (BPW) and homogenized One or more 10fold dilutions (according to the expected level of contamination) are prepared in BPW Aliquots (10 ml) of this initial dilution are transferred to three tubes Then × ml of the initial dilution are added to ml of BPW and × ml of each further dilution are added to ml of BPW These tubes are incubated 37 °C (or 30 °C)1) for 18 h ± h 4.2.2 Enrichment in selective liquid medium Tubes of liquid enrichment broth (EE broth) are inoculated with each tube of culture obtained after preenrichment (at least × 3) The tubes are incubated at 37 °C (or 30 °C)1) for 24 h ± h 4.2.3 Isolation and selection for confirmation A selective solid medium (violet red bile glucose agar) is inoculated with a loop from each of the incubated cultures obtained after enrichment in EE broth, then incubated at 37 °C (or 30 °C)1) It is examined after 24 h ± h to check for the presence of colonies presumed by their characteristics to be Enterobacteriaceae 4.2.4 Confirmation Colonies of presumptive Enterobacteriaceae are subcultured on non-selective medium, then confirmed by means of tests for the fermentation of glucose and the presence of oxidase 4.2.5 Calculation The most probable number of Enterobacteriaceae per millilitre or per gram of the test sample is calculated from the number of confirmed positive tubes using the MPN table (see ISO 7218) Diluent, culture media and reagent For current laboratory practice, see ISO 7218 and ISO/TS 11133-1 and ISO/TS 11133-2 5.1 Diluent: buffered peptone water (BPW) See ISO 6887-1:1999, 5.2.2 BPW is used as the non-selective pre-enrichment medium for the enumeration method © ISO 2004 – All rights reserved Copyright International Organization for Standardization Reproduced by IHS under license with ISO No reproduction or networking permitted without license from IHS Not for Resale `,,,,,,-`-`,,`,,`,`,,` - 4.1.3 ISO 21528-1:2004(E) 5.2 Culture media 5.2.1 Enrichment medium: Buffered brilliant green bile glucose broth (EE broth) 5.2.1.1 Composition Enzymatic digest of animal tissues 10,0 g Glucose 5,0 g Disodium hydrogen phosphate (Na2HPO4) 6,45 g Potassium dihydrogen phosphate (KH2PO4) 2,0 g Beef bile for bacteriological use 20,0 g Brilliant green (bacteriological quality) 0,0135 g Water 000 ml 5.2.1.2 Preparation Dissolve the components or the dehydrated complete medium in the water by boiling Do not heat the medium for longer than 30 Cool the medium rapidly Adjust the pH, if necessary, so that after boiling it is 7,2 ± 0,2 at 25 °C Dispense the medium in 10 ml amounts into sterile tubes of appropriate capacity (6.5) Do not sterilize the medium The medium may be stored for up to month at °C ± °C 5.2.1.3 Performance testing for the quality assurance of the culture medium For the definition of selectivity and productivity, refer to ISO/TS 11133-1 For the performance criteria, refer to ISO/TS 11133-2:2003, Table B.3 5.2.2 Violet red bile glucose (VRBG) agar 5.2.2.1 Components Enzymatic digest of animal tissues 7,0 g Yeast extract 3,0 g Bile salts No 1,5 g Glucose 10,0 g Sodium chloride 5,0 g Neutral red 0,03 g Crystal violet 0,002 g Agar g to 18 ga) Water 000 ml a) Depending on the gel strength of the agar `,,,,,,-`-`,,`,,`,`,,` - Copyright International Organization for Standardization Reproduced by IHS under license with ISO No reproduction or networking permitted without license from IHS © ISO 2004 – All rights reserved Not for Resale ISO 21528-1:2004(E) 5.2.2.2 Preparation Dissolve the components or the dehydrated complete medium in the water by boiling Adjust the pH, if necessary, so that after boiling it is 7,4 ± 0,2 at 25 °C Dispense the culture medium into sterile tubes or flasks (6.5) of appropriate capacity `,,,,,,-`-`,,`,,`,`,,` - Do not sterilize the medium Use the molten medium within h of its preparation 5.2.2.3 Preparation of agar plates Immediately transfer approximately 15 ml of the culture medium, cooled to between 44 °C and 47 °C (6.4), to Petri dishes (6.7) and allow to solidify Just before use, dry the plates, preferably with the lids off and the agar surface downwards, in a drying cabinet (6.3) until the agar is dry If prepared in advance, the undried plates may be stored in conditions that not change their composition for up to weeks at °C ± °C 5.2.2.4 Performance testing for the quality assurance of the culture medium For the definition of selectivity and productivity, refer to ISO/TS 11133-1 For the performance criteria, refer to ISO/TS 11133-2:2003, Table B.1 5.2.3 5.2.3.1 Nutrient agar Composition Meat extract 3,0 g Enzymatic digest of animal tissues 5,0 g Sodium chloride 5,0 g Agar g to 18 g a) Water 000 ml a) Depending on the gel strength of the agar 5.2.3.2 Preparation Dissolve the components or the dehydrated complete medium in the water, by heating if necessary Adjust the pH, if necessary, so that after sterilization it is 7,3 ± 0,2 at 25 °C Dispense the culture medium into sterile tubes or flasks (6.5) of appropriate capacity Sterilize for 15 in an autoclave (6.1) set at 121 °C 5.2.3.3 Preparation of agar plates Transfer portions of about 15 ml of the culture medium, melted and cooled to approximately 47 °C, to Petri dishes (6.7) and allow to solidify © ISO 2004 – All rights reserved Copyright International Organization for Standardization Reproduced by IHS under license with ISO No reproduction or networking permitted without license from IHS Not for Resale ISO 21528-1:2004(E) Just before use, dry the plates, preferably with the lids off and the agar surface downwards, in a drying cabinet (6.3) until the agar is dry If prepared in advance, the undried plates may be stored in conditions that not change their composition for up to weeks at °C ± °C 5.2.3.4 Performance testing for the quality assurance of the culture medium For the definition of selectivity and productivity, refer to ISO/TS 11133-1 For the performance criteria, refer to ISO/TS 11133-2:2003, Table B.6 5.2.4 Glucose agar 5.2.4.1 Composition Enzymatic digest of casein 10,0 g Yeast extract 1,5 g Glucose 10,0 g Sodium chloride 5,0 g Bromocresol purple 0,015 g Agar g to 18 g a) Water 000 ml Depending on the gel strength of the agar 5.2.4.2 Preparation Dissolve the components or the dehydrated complete medium in the water, by heating if necessary Adjust the pH, if necessary, so that after sterilization it is 7,0 ± 0,2 at 25 °C Dispense the culture medium in tubes (6.6) of appropriate capacity (e.g 10 ml of culture medium for tubes of 16 mm × 160 mm) Sterilize for 15 in an autoclave (6.1) set at 121 °C Leave the tubes in a vertical position The medium may be stored for up to week at °C ± °C In order to remove oxygen, just before use, heat the medium in boiling water or flowing steam for 15 min, then cool rapidly to the incubation temperature 5.3 Oxidase reagent 5.3.1 Composition N,N,N',N'-Tetramethyl-p-phenylenediamine dihydrochloride Water 5.3.2 1,0 g 100 ml Preparation Dissolve the component in the cold water Prepare the reagent just before use Commercially available disks or sticks may be used In this case, follow the manufacturer's recommendations Copyright International Organization for Standardization Reproduced by IHS under license with ISO No reproduction or networking permitted without license from IHS © ISO 2004 – All rights reserved Not for Resale `,,,,,,-`-`,,`,,`,`,,` - a) ISO 21528-1:2004(E) Apparatus and glassware Usual microbiological laboratory apparatus and, in particular, the following (see ISO 7218) 6.1 Apparatus for dry sterilization (oven) or wet sterilization (autoclave) See ISO 7218 6.2 Incubator, capable of operating at 37 °C ± °C 6.3 Drying cabinet (ventilated by convection) or incubator, capable of operating between 37 °C and 55 °C 6.4 Water bath, or similar apparatus, capable of being maintained at between 44 °C and 47 °C 6.5 Containers (e.g bottles, tubes, flasks), suitable for the sterilization and storage of culture media `,,,,,,-`-`,,`,,`,`,,` - 6.6 Test tubes, of dimensions 16 mm × 160 mm and 20 mm × 200 mm, and flasks or bottles of capacity between 150 ml and 500 ml 6.7 Petri dishes, made of glass or plastics, of diameter 90 mm to 100 mm 6.8 Loops (of diameter approximately mm) and wires, made of platinum/iridium or nickel/chromium, or glass rods, or equivalent sterile disposable loops or inoculating needles 6.9 Graduated pipettes, of ml nominal capacity, graduated with 0,1 ml divisions, and with an outflow opening of appropriate diameter 6.10 pH-meter, accurate to within ± 0,1 pH unit at 25 °C 6.11 Homogenizer See ISO 7218 Sampling It is important that the laboratory receive a sample which is truly representative of the product and has not been damaged or changed during transport or storage Sampling should be carried out in accordance with the specific International Standard appropriate to the product concerned If there is no specific International Standard, it is recommended that agreement be reached on this subject by the parties concerned Preparation of test sample Prepare the test sample in accordance with ISO 6887-1, ISO 6887-2, ISO 6887-3, ISO 6887-4 or ISO 8261, and/or the specific International Standard appropriate to the product concerned If there is no specific International Standard, it is recommended that agreement be reached on this subject by the parties concerned 9.1 Procedure General See ISO 7218 © ISO 2004 – All rights reserved Copyright International Organization for Standardization Reproduced by IHS under license with ISO No reproduction or networking permitted without license from IHS Not for Resale ISO 21528-1:2004(E) The culture media are usually incubated at 37 °C Alternatively, an incubation temperature of 30 °C may be used.1) 9.2 Detection method 9.2.1 Test portion and initial suspension Take a test portion (x g or x ml) according to the sensitivity required and homogenize in 9x ml of buffered peptone water (5.1) Transfer the appropriate volume to a sterile tube or container (6.5) according to the limit of detection required 9.2.2 Non-selective pre-enrichment Incubate the initial suspension (9.2.1) at 37 °C for 18 h ± h 9.2.3 Selective enrichment Transfer ml of the culture obtained in 9.2.2 to a tube containing 10 ml of the enrichment medium (5.2.1) Incubate the inoculated medium at 37 °C for 24 h ± h Continue the procedure with isolation and selection for confirmation (9.4) 9.3 Enumeration method (MPN method) 9.3.1 Test portion, initial suspension and further dilutions Depending on the desired accuracy of the results, inoculate an appropriate number of flasks or tubes with the same dilution (e.g three, five or ten flasks or tubes) As a general rule, the techniques specified require three flasks or tubes per dilution For preparation of the initial suspensions and further dilutions, use the diluent (5.1) To prepare the initial suspension, take a test portion of x g or x ml and homogenize in x ml of buffered peptone water (BPW) (5.1) A 10–1 dilution is thus obtained 10 ml of the 10–1 dilution contain the equivalent of g or ml of sample NOTE `,,,,,,-`-`,,`,,`,`,,` - Prepare further dilutions by taking ml of the 10–1 dilution and add to ml of BPW Repeat to make further necessary decimal dilutions Transfer three 10 ml volumes of the 10–1 suspension to tubes (6.5) Transfer three ml volumes of each subsequent dilution to tubes containing ml of BPW (see Annex B) 9.3.2 Non-selective pre-enrichment Incubate the initial suspensions and dilutions (total tubes) (see 9.3.1) at 37 °C for 18 h ± h 9.3.3 Selective enrichment Transfer ml of the cultures obtained in 9.3.2 to tubes containing 10 ml of the enrichment medium (5.2.1) Incubate the inoculated media at 37 °C for 24 h ± h Copyright International Organization for Standardization Reproduced by IHS under license with ISO No reproduction or networking permitted without license from IHS © ISO 2004 – All rights reserved Not for Resale ISO 21528-1:2004(E) 9.4 9.4.1 Isolation and selection for confirmation Isolation 9.4.2 Selection of colonies for confirmation Characteristic colonies are pink to red or purple (with or without precipitation haloes) From each of the incubated plates (see 9.4.1) on which characteristic colonies have developed, choose a well-isolated characteristic colony for subculturing (see 9.5) for the biochemical confirmation tests (see 9.6) If more than one morphology is present in the colonies, select one colony of each morphology for subculture Certain Enterobacteriaceae may cause decoloration of their colonies or of the medium Therefore, when no characteristic colonies are present, choose whitish colonies for confirmation 9.5 Subculturing selected colonies Streak onto nutrient agar plates (5.2.3) each of the colonies selected for confirmation (see 9.4.2) Incubate these plates at 37 °C for 24 h ± h Select a well-isolated colony from each of the incubated plates for the biochemical confirmation tests (see 9.6) 9.6 9.6.1 Biochemical confirmation tests Oxidase reaction Using a platinum/iridium loop, wire or glass rod (6.8), take a portion of each well-isolated colony (see 9.5) and streak onto a filter paper moistened with the oxidase reagent (5.3) or onto a commercially available disc A nickel/chromium loop or wire shall not be used Consider the test to be negative if the colour of the filter paper does not turn dark within 10 s Consult the manufacturer's instructions for ready-to-use discs 9.6.2 Fermentation test Using a wire (6.8), stab the same colonies selected in 9.5 that gave a negative oxidase test into tubes containing glucose agar (5.2.4) Incubate these tubes at 37 °C for 24 h ± h If a yellow colour develops throughout the contents of the tube, regard the reaction as being positive 10 Expression of results 10.1 Confirmed positive tubes If any of the selected typical colonies (see 9.4.2) from a subculture (see 9.4.1) is oxidase-negative and glucose-positive, the tube from which the subculture was derived shall be regarded as being positive for Enterobacteriaceae © ISO 2004 – All rights reserved Copyright International Organization for Standardization Reproduced by IHS under license with ISO No reproduction or networking permitted without license from IHS Not for Resale `,,,,,,-`-`,,`,,`,`,,` - Using a loop (6.8), streak from the incubated enrichment medium (see 9.2.3) or from each of the incubated tubes (see 9.3.3) the surface of a plate containing the selective medium (5.2.2) and incubate the plate at 37 °C for 24 h ± h ISO 21528-1:2004(E) 10.2 Detection method In accordance with the results of the interpretation (see 10.1), indicate the presence or absence of Enterobacteriaceae in a test portion of x g or x ml of product (see ISO 7218) 10.3 Enumeration method: Calculation of the most probable number (MPN) Calculate the most probable number from the number of positive tubes at each dilution See ISO 7218:1996, 9.4 11 Precision It is known that wide variations in results can occur with the MPN technique Results obtained by this method should therefore be used with caution Confidence limits are given in ISO 7218:1996, Annex A 12 Test report The test report shall specify: all information necessary for the complete identification of the sample; the sampling method used, if known; the test method used, with reference to this part of ISO 21528; the incubation temperature used; all operating details not specified in this part of ISO 21528, or regarded as optional, together with details of any incidents which may have influenced the test results; the test results obtained `,,,,,,-`-`,,`,,`,`,,` - 10 Copyright International Organization for Standardization Reproduced by IHS under license with ISO No reproduction or networking permitted without license from IHS © ISO 2004 – All rights reserved Not for Resale ISO 21528-1:2004(E) Annex A (normative) Diagram of procedure of the detection method `,,,,,,-`-`,,`,,`,`,,` - 11 © ISO 2004 – All rights reserved Copyright International Organization for Standardization Reproduced by IHS under license with ISO No reproduction or networking permitted without license from IHS Not for Resale ISO 21528-1:2004(E) Annex B (normative) Diagram of procedure for MPN technique `,,,,,,-`-`,,`,,`,`,,` - 12 Copyright International Organization for Standardization Reproduced by IHS under license with ISO No reproduction or networking permitted without license from IHS © ISO 2004 – All rights reserved Not for Resale `,,,,,,-`-`,,`,,`,`,,` - Copyright International Organization for Standardization Reproduced by IHS under license with ISO No reproduction or networking permitted without license from IHS Not for Resale ISO 21528-1:2004(E) ICS 07.100.01 Price based on 12 pages `,,,,,,-`-`,,`,,`,`,,` - © ISO 2004 – Allforrights reserved Copyright International Organization Standardization Reproduced by IHS under license with ISO No reproduction or networking permitted without license from IHS Not for Resale